I have seen many large size call center who have invested so much in other things but using unmanaged switches. Unprofessional Network Admins tend to use unmanaged switches as they please their owner with “cheap solution” saying they got buy for the buck! Indeed unmanaged switches do not have any intelligence in them, and can cause traffic congestion in a busy call center network (including under 10 seat call center)

Not paying attention to what lies between Switches and (Servers)

Yes I mean Network cable, RJ45 connector and mixing Network cable with electricity cables are deadly mistakes. OK Server is very fast and you have got smart switches (instead of stupid dumb switches) poor quality cables and even connectors can cause bottle-neck problem. Buying AMP china copper version is utter waste of money. It might be 3 times cheaper than original brand but same time it can be 10X more problematic or maybe 100 times. A big no-no for such variants. Always buy original brand. Never listen to stories of vendors they have used low-price cable on such and such place. Same goes with RJ45 connectors, Ios etc. Do not compromise on tiny things that binds entire network together.

Not Separating other-Data with Voice-data

If there’s single basic networking concept that hangs as a dark unknown in most Network Admin minds, it’s VLANs. If your IT guy can’t wrap his head around them, he is not alone. I do not like to go into technicalities as I intend to write for call center owners (non-technical mostly) You have got to separate your voice and data. If you happen to use FTH (Fiber to home ) service then they charge for volume use so it is better to use browsing on uncapped (home package like connection) and Voice from capped (business class dedicated network) it is straight financial benefit. Beside money saving it will improve VoIP quality remarkably. Of course you need 2 Port ONT or two internet connections from same or different ISP to separate Voice and Data.